[DaveK]

Over the past 15 months or so that I've owned my 2000 M5, it's needed quite a bit of work, luckily under CPO warranty. First it wouldn't pass CA smog, and needed both cats replaced. Then it spewed oil into the intake plenum, ducts, and air boxes, and a bunch of VANOS seals had to be replaced. It also needed a fix for the ventilation blower not working and a couple other minor things. The SES light came on occasionally but the dealer was unable to diagnose it for a while, then they replaced one of the cats again a couple months ago. The light came on again and a couple weeks ago and they replaced one of the VANOS units. The car seems to have been getting gradually 'twitchier' in low gear at low rpm lately and I'm not sure the new VANOS has fixed that, although it seems better and the SES light stayed off, until something strange happened this past weekend:

I was driving on the highway when the SES light suddenly came on and the car immediately lost a bunch of power. This was near the end of a road trip totaling a couple hundred miles. I immediately checked all the gauges and they were normal. For the first 10 seconds or so it seemed only to be down on power but otherwise running OK, as if it went into a limp mode. I started moving toward the right lane, and then it started running rough and lost even more power, and continued getting worse. I put the flashers on and limped it to the next exit, luckily it was close and there was a gas station right there. I pulled in and let it idle a bit, then revved it some (to maybe 2500 rpm) and it was still running rough so I shut it off and checked under the hood. Everything looked normal, so after a minute or two I started it up again and it ran fine, with no SES light. I drove it around the gas station lot a bit to make sure it was OK, then got back on the highway and drove home with no incident. I'm glad it's running OK now, but I'm concerned that it could happen again at any time. I left a message at the dealer today, but haven't heard back yet. Has anyone else had any mysterious issues like this that occurred without warning and for no obvious reason, then disappeared?

I assume it left codes in the computer that can be retrieved to help diagnose it, and hopefully the dealer will be willing to look at it without the CPO co-payment or other fees since they worked on it so recently and it could be related.

- Dave


PS: I don’t want to sound too negative about the car. For the most part it seems to have been running fine, and while it's not been at the dealership I've really enjoyed it. Luckily even with the problems it hasn't stranded me yet, although I thought it would for a minute last weekend. However, I am concerned about future repairs once the CPO warranty runs out next year. Hopefully anything else that's going to break will do so before then.

 

[stever]

there seem to be a variety of things that make the M5 go into limp-home. and all that i have encountered can at least temporarily be solved by turning the ignition off and back on

running up against the rev limiter a couple times will turn on limp-home, but in your case, i'd suspect either one of the cam sensors which aren't terribly reliable, or the twitchiness in low also sounds like one or both mass air flow sensors which are similarly unreliable -- if they weren't replaced after the oiling incident are very likely culprits (they are covered by the 80k emissions warranty as well)

the error codes are not terribly informative of the actual problem and need to be interpreted by someone with experience

 

[martybm5]

I've had the same thing happen to me. Do a search and you'll find a few references to this happening. Try searching for MAFS. You can clean the MAFS yourself in about 30 mins and it will help.

Take a look at this http://www.louv.tv/cars/m5/MAF/
instructions on how to clean MAFS.

 

[DaveK]

Thanks for the suggestions. Both MAFS and both air filters were replaced after the oil problem so I'd be surprised if the MAFS were dirty already. I didn't run up against the rev limiter, I barely got it over 5K all day, mostly highway cruising in 6th.

Maybe something did get the MAFS dirty (maybe when they did the VANOS work), or maybe a sensor is faulty or the wiring loose. On the other hand, I did find references to others who had similar occurrences that were apparently random and isolated, and not a real problem. Unless the dealer wants to check it, I'll wait and see if it happens again.

The fact that it's been going through catalytic converters concerns me though. Wouldn't that indicate that it's not running as well as it should, maybe too rich and burning them up? Even after both cats were replaced it only just barely passed smog, then burned another one up within a year. And I'm only 5K from the emissions warranty expiring.

- Dave

 

[DavidS]

Get them to replace the cam sensors. Those were later redesigned to be more reliable. With a MY 2000 car cam sensor replacment is not an "if" question, it is a "when" question.

David